1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a microwave oven having a cooling arrangement which can be easily assembled and fabricated on a rear wall of the microwave oven with reduced noise, improved cooling efficiency, and increased space efficiency of a machine chamber thereof.
2. Description of the Prior Art
In general, a microwave oven has a heating chamber for heating food, and a machine chamber for supplying heat into the heating chamber. Numerous components such as a magnetron to generate heat of high temperature into the heating chamber are provided in the machine chamber. Since a large quantity of high-temperature heat is produced by not only the magnetron but also such components as a high voltage transformer and the like while the microwave oven is operated, it may be necessary to introduce air into the machine chamber in order to cool these components. Further, introduction of air into the machine chamber can also be necessary according to cooking modes of the microwave oven.
In order to cool the magnetron or ventilate the heating chamber as described above, in the machine chamber are disposed a fan motor and a cooling fan rotated by the fan motor to blow air into the machine chamber.
Referring to FIGS. 1 through 3 schematically showing a construction of a conventional cooling arrangement of a microwave oven device having a fan motor, there are disposed a magnetron 12, a high voltage transformer 11, and numerous components (not shown) such as a PCB substrate and a high voltage condenser and the like in a machine chamber 10. Plural pores 31 are formed on a rear wall 20 of machine chamber 10. A fan motor 32 is fixed on a middle portion of pores 31 by a screw and the like, and a cooling fan 33 is fixed on the rotation shaft of fan motor 32. A wind guide 34 is fixedly disposed on rear wall 20 to surround the upper, lower and front sides of cooling fan 33 and fan motor 32, and has an opening formed at the center thereof in alignment with cooling fan 33 in order for wind to pass therethrough.
In the above described conventional cooling arrangement, as shown in FIG. 2, when fan motor 32 has been activated, air is introduced through plural pores 31 and the opening formed on wind guide 34 into machine chamber 10. At that time, the air is concentrated on cooling fan 33 disposed at the center thereof making noise due to compression of the air. Besides, the introduced air may cause bigger noise because the stream of the air is at a slant and thereby the rim of respective pore 31 interferes with the stream of the introduced air. In this case, the nearer the outer periphery of the rear wall the pores are, the greater the slant of the stream of and the resistance to the air passing through the pores are and thereby the bigger the noise is.
Meanwhile, after the cold air having been introduced into machine chamber 10 by the rotation of the cooling fan 33 cools high voltage transformer 11 and magnetron 12, a part of the air is introduced into the heating chamber, and the rest of the air flows in machine chamber 10 for cooling the exterior of the heating chamber, and then is exhausted through exhaust holes formed on the rear wall and a base plate of the microwave oven. However, since the opposite sides of wind guide 34 are open, the heated air obtained by cooling high voltage transformer 11 and magnetron 12 in the machine chamber is re-introduced into the back of cooling fan 33 and blown by cooling fan 33 again, so as to make the cooling efficiency of the cooling arrangement considerably reduced.
Further, in the conventional device, cooling fan 33 and fan motor 32 surrounded by wind guide 34 are disposed in machine chamber 10 to occupy much space of machine chamber 10, and accordingly it is difficult to assemble them in machine chamber 10 due to interference of the neighboring components such as the magnetron, high voltage transformer, high voltage condenser, and the like.
Moreover, the back of the microwave oven should not be in close contact with a neighboring wall or other obstacles in order for the exterior air to flow thereinto. Therefore, a spacer 40 for ensuring a minimum space between the neighboring obstacles and the back of the microwave oven should be provided in the cooling arrangement as shown in FIG. 3.
To manufacture rear wall 20 having a plurality of pores 31, five complicated steps must be performed as follows:
drawing, cutting, notching, and piecing the rear wall in order for other plates to be assembled thereon;
pressing the notched and pieced rear wall to perforate pores therein, which pressing process is repeated three times because the pores are concentrated in a limited area and formed directly at the rear wall of the microwave oven; and
bending the edges of the perforated rear wall to complete the manufacture of the rear wall.
Therefore, the number of manufacturing steps of the rear wall is so large that the manufacturing cost thereof is increased and accordingly the quality thereof is deteriorated.